Cope holder device

ABSTRACT

An upper die holder apparatus having a holder body has an upper die clamp supported to the holder body with a supporting point supporting the upper die clamp in a vicinity of a center in a vertical direction of the holder body. A clamping force applier is provided to the holder body for pressing an upper portion of the upper die clamp so that the upper die clamp clamps the upper die. A pressure receiver is provided to an upper portion of the upper die clamp. The pressure receiver, having a pressure sensing surface, is provided so that its advancing and retreating are adjusted to a pressing direction by the clamping force applier and the pressure receiver is provided so that an opening amount of the upper die clamp at the time of unclamping is freely selected between a plurality of stages.

TECHNICAL FIELD

The present invention relates to upper die holder apparatus in a pressbrake, and more specifically relates to the upper die holder apparatuswhich is capable of easily attaching/detaching an upper die to/from anupper table in the press brake so as to replace it.

BACKGROUND ART

Conventionally, press brakes are constituted so that an upper table(occasionally called as an upper apron) and a lower table (occasionallycalled as a lower apron) are opposed to each other in a verticaldirection, and suitable one of the upper table and the lower table isdriven up and down as a ram.

In the press brakes having the above constitution, in order to bend aplate shaped workpiece, a lower die (die) is attached to an upperportion of the lower table and an upper die (punch) is attached to alower portion of the upper table.

In the above constitution, after a workpiece is located on the lowerdie, the upper die is engaged with the lower die so that the workpiececan be bent.

Incidentally, in press brakes, in order to replace the upper dieaccording to a difference in bending forms or the like of workpieces,for example, many upper die holder apparatuses are attached to the lowerportion of the upper table, and these upper die holder apparatusessupport the upper die to the upper table so that the upper die can bedetached and replaced.

With reference to FIGS. 1 and 2, a prior upper die holder apparatus 101is provided with a holder body 105 which is attached to an upper table103 detachably, an upper die supporting section 109 for supporting anupper die 107 is provided so as to be integral with a lower portion ofthe holder body 105, and an upper die clamp 111 which freely presses andfixes an upper portion of the upper die 107 to the holder supportingsection 109 is supported to the holder body 105 in a rocking manner witha vicinity of an approximately center in a vertical direction being as asupporting point.

Further, a pressing member 113 for pressing the upper die 107 againstthe upper die supporting section 109 is provided to a lower portion ofthe upper die clamp 111, a wedge piece 115 (locking member) which freelylocks into a drop-proof groove 107G provided to the upper die 107 isprovided below the pressing member 113 so as to freely advance andretreat, and is biased to a direction of the upper die supportingsection 109 by a resilient member 117. An inclined plane 115S is formedon an upper surface of a tip of the wedge piece 115 so as to be easilyengaged with and detached from the drop-proof groove 107G. The wedgepiece 115 is composed of a plurality of wedge piece dividing pieces.

Further, a clamping force applying means 119 for pressing the upperportion of the upper die clamp 111 so as to apply a clamping force forclamping the upper die 107 via the upper die clamp 111 is provided tothe holder body 105.

The clamping force applying means 119 is included in a cylinder 121 of afront-rear direction provided to the holder body 105, and two pistons123 are provided slidably in the cylinder 121 in the front-reardirection. Pin-shaped pusher sections 125 are projected respectivelyfrom the pistons 123 towards the outside, and the pusher sections 125are projected outward. Tips of the pusher sections 125 can touch andseparate from a pressing screw 127 as a pressure receiving sectionprovided to the upper portion of the upper die clamp 111.

Further, a resilient member 129 such as a coil spring for always biasingthe piston 123 so as to always press the piston 123 inward is woundaround the pusher sections 125 of the pistons 123. Moreover, an oilpassage 131 which communicatively connects to an inside of the cylinder121 is formed on the holder body 105, and the oil passage 131 iscommunicatively connected with a pressure oil supply source (not shown)via a hydraulic hose 133.

In addition, an adapter plate 135 having a divergent notched portion onits lower center is mounted integrally to a front surface of the holderbody 105. The adapter plate 135 touches a front lower portion of theupper table 103, and a clamp jaw 139 is clamped by a clamping bolt 137screwed up to the upper table 103 so that the adapter plate 135 ispressed and fixed to the upper table 103. As a result, the holder body105 is mounted to the upper table 103.

In order to adjust a vertical position (height position) of the holderbody 105, a wedge member 141 lies between an upper surface of the holderbody 105 and a lower surface of the upper table 103 so that its positionis freely adjusted to a horizontal direction, and a fixing bolt 145which pierces a slot 143 in the horizontal direction provided on theadapter plate 135 is screwed up into the wedge member 141.

In the prior constitution, therefore, when upper die 107 is detachedfrom the upper table 103 so as to be replaced, the pusher sections 125of the pistons 123 in the cylinder 121 are retreated so that the upperdie clamp 111 is in an unclamped state. The wedge piece 115 (a pluralityof wedge piece dividing pieces) which is biased by the resilient member117 is hooked on the drop-proof groove 107G of the upper die 107 so thatthe in upper die 107 it held. When the upper die 107 is front-removedthe upper die 107 is twisted so that the wedge piece 115 is retreatedagainst the biasing force of the resilient member 117 and the upper die107 is removed.

Further, at the time of attaching, namely, first-feeding the upper die107, when the upper die 107 is inserted between the upper die supportingsection 109 of the holder body 105 and the upper die clamp 111 from alower side, the wedge piece 115 is retreated against the biasing forceof the resilient member 117 and then is advanced again by the resilientmember 117 so as to be hooked onto the drop-proof groove 107G of theupper die 107 and the upper die 107 is held.

At the time of replacing the upper die 107, however, when a strongerforce than the biasing force of the resilient member 117 is applied tothe upper die 107 in such a manner that the upper die 107 is slidmightily or a twisting force is suddenly applied to the die, there is adanger such that the upper die 107 drops even when it is not front-fedand front-removed.

The present invention is devised in order to solve the above problem,and an object of the invention is to provide an upper die holderapparatus which is capable of easily detaching an upper die from a pressbrake and replacing it, and moving the upper die to a horizontaldirection without a danger such that the upper die drops particularlywhen the upper die is not front-fed and front-removed.

DISCLOSURE OF THE INVENTION

In order to achieve the above object, an upper die holder apparatus ofthe present invention based on a first aspect includes: a holder body;an upper die supporting section provided to a lower portion of theholder body, the upper die supporting section for supporting an upperdie; an upper die clamp supported to the holder body in a rockingmanner, the upper die clamp being supported in a rocking manner with avicinity of a center in a vertical direction of the holder body being asa supporting point; a pressing member provided to a lower portion of theupper die clamp, the pressing member for pressing the upper die againstthe upper die supporting section; a locking member provided to a lowerportion of the upper die clamp, the locking member being biased towardsthe upper die supporting section so as to freely lock into a drop-proofgroove provided to the upper die; clamping force applying means providedto the holder body, the clamping force applying means pressing an upperportion of the upper die clamp so that the upper die clamp clamps theupper die; and a pressure receiving member provided to an upper portionof the upper die clamp, the pressure receiving member having a pressuresensing surface to be pressed by the clamping force applying means. Inthe above constitution, the pressure receiving member is provided sothat its advancing and retreating are adjusted to a pressing directionby the clamping force applying means, and the pressure receiving memberis provided so that an opening quantity of the upper die clamp at thetime of unclamping is freely selected between a plurality of stages.

Therefore, since the a position of the pressure sensing surface of thepressure receiving member can be selected from a plurality of stages,the opening quantity of the upper die clamp at the time of unclampingcan be switched between a plurality of stages by a simple operation.When the upper die is not front-fed and front-removed, for example, theopening quantity is set to be small, so that the upper die can be movedto a lateral direction without a danger such that of dropping. When theopening quantity is set to large, suitable one of both left and rightsides of the upper die is inclined downward, the upper die is pushedeasily against the biasing force of the locking member andsimultaneously the upper die is front-fed and front-removed easily.

In an upper die holder apparatus of the present invention based on asecond aspect depending from the upper die holder apparatus based on thefirst aspect, the opening quantity of the upper die clamp at the time ofunclamping is adjustable so that a locked state between the lockingmember and the drop-proof groove of the upper die is freely selectedfrom a first stage where the upper die cannot be drawn downward and asecond stage where the upper die can be drawn downward.

Therefore, when the upper die is not front-fed and front-removed,therefore, the opening quantity is set to the first stage so that theupper die can be moved to a lateral direction without a danger ofdropping. When the opening quantity is set to the second stage, theupper die is easily front-fed and front-removed.

In an upper die holder apparatus of the present invention based on athird aspect depending from the upper die holder apparatus based on thefirst or second aspect, the pressure receiving member is screwed intothe upper portion of the upper die clamp, and a position lever which isrotated so as to advance and retreat the pressure receiving membergradationally is provided to the pressure receiving member.

Therefore, since a position of the pressure sensing surface of thepressure receiving member is switched gradually between the pluralstages only by a simple operation for rotating the position lever, theopening quantity of the upper die clamp at the time of unclamping iseasily switched between the plural stages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of FIG. 2 illustrating a prior example: aleft side with respect to a center line illustrates a state that anupper die clamp is opened: and a right side illustrates a state that theupper die clamp clamps an upper die.

FIG. 2 is a front view of an upper die holder apparatus according to aprior example.

FIG. 3 is a partially sectional view of a mode of the present inventionillustrating a first-stage switching state by means of a position leverwhen the upper die clamp is in an unclamped state.

FIG. 4 is a partially sectional view of the mode of the presentinvention illustrating a second-stage switching state by means of theposition lever when the upper die clamp is in the unclamped state.

FIG. 5 shows the mode of the present invention: a right side withrespect to an extended line of a center line drawn on an upper part is asectional view taken in the direction of the arrow along the line V—V inFIG. 6 that illustrate a state that the upper die clamp clamps the upperdie; and a left side with respect to the extended line of the centerline is a sectional view taken in the direction of the arrow along theline V′–V in FIG. 6 that illustrates a state that the upper die clamp isopened.

FIG. 6 is a front view of the upper die holder apparatus illustratingthe mode of the present invention.

FIG. 7 is a sectional view taken in the direction of the arrow along theline VII—VII in FIG. 3.

FIG. 8 is a partially sectional view of a lower portion of the upper dieclamp.

THE BEST MODE FOR CARRYING OUT THE INVENTION

Modes of an upper die holder apparatus and a method of removing an upperdie from the upper die holder apparatus according to the presentinvention are explained below with reference to the drawings.

With reference to FIGS. 5 and 6, an upper die holder apparatus 1 of thismode is attached detachably to a lower portion of an upper table 3 in apress brake (an entire constitution is not shown). Many upper die holderapparatuses 1 are attached to the lower portion of the upper table 3 ina horizontal direction with suitable intervals.

That is to say, an upper die 5 in the press brake is composed of oneupper die which is long in a horizontal direction (in FIG. 5, adirection vertical to a sheet surface, and in FIG. 6, the horizontaldirection), or a plurality of divided type upper dies having differentlengths which are suitably combined to be used. In order to cope withboth the cases, the many upper die holder apparatuses 1 are attached tothe upper table 3 with suitable intervals.

As is clear from FIG. 5, the upper die holder apparatus 1 is constitutedso as to include a holder body 7 which is detachably attached to theupper table 3, an upper die clamp 11 which freely presses and fixes anupper portion 5U of the upper die 5 to an upper die supporting section 9provided integrally with a lower portion of the holder body 7, clampingforce applying means 13 for applying a clamping force to the upper dieclamp 11, clamp switching means 15 for freely transmitting and removingthe clamping force by the clamping force applying means 13 to/from theupper die clamp 11, upper die clamp holding means 17 for holding theupper die clamp 11 to a lower portion of the holder body 7 in a rockingmanner, and releasing state holding means 19 (see FIG. 6) for freelyholding the upper die clamp 11 in a state that the clamp of the upperdie 5 is released.

More specifically, the holder body 7 has the upper die supportingsection 9 with thin thickness which is integral with a lower portion ofa block section 7B which is thick in a front-rear direction. An adapterplate 25 which projects upward is attached integrally to a front surface(in FIG. 5, a left surface) of the block section 7B of the holder body 7by a plurality of bolts 21 and pins 23 (see FIG. 6).

The adapter plate 25 has, as shown in FIG. 6, a divergent notchedportion on its lower center. As shown in FIG. 5, a rear surface of theupward projected portion of the adapter plate 25 touches a front lowerportion of the upper table 3, a clamp jaw 29 is clamped by a clampingbolt 27 screwed up into the upper table 3, and the upward projectedportion of the adapter plate 25 is pressed and fixed to the upper table3, so that the holder body 7 can be attached to the upper table 3.

A locking section 31 projects from a rear surface of a lower portion ofthe clamp jaw 29, and a hooking section 33 which can be hooked on thelocking section 31 projects from a front surface of the upward projectedportion of the adapter plate 25. When the holder body 7 is attached,therefore, even if the clamping bolt 27 is loosened, the hooking section33 of the adapter plate 25 is engaged with the locking section 31 of theclamp jaw 29, thereby preventing the adapter plate 25 from dropping.

In order to adjust a vertical position (height position) of the holderbody 7, a wedge member 35 lies between an upper surface of the holderbody 7 and a lower surface of the upper table 3 so that its position isfreely adjusted to the horizontal direction in FIG. 5, and a fixing bolt39 which pierces an insertion hole 37 provided on the adapter plate 25is screwed into the wedge member 35.

In the above constitution, the clamp jaw 29 is maintained to be clampedloosely so that the holder body 7 does not drop, and the wedge member 35is adjusted to the horizontal direction in FIG. 5 in a state that thefixing bolt 39 is loosened, thereby finely adjusting the holder body 7up and down with respect to the upper table 3.

The upper die clamp 11 is composed of a plate shaped member havingapproximately same width as a width of the holder body 7 in thehorizontal direction, and a corresponding upward projected portion isformed on a portion of the adapter plate 25 corresponding to thedivergent notched portion. In order to press and fix the upper section5U of the upper die 5 between the upper die supporting section 9 and theupper die clamp 11, the upper die 5 is supported to the holder body 7 bythe upper die clamp holding means 17 in a rocking manner.

More specifically, in the upper die clamp holding means 17, a pluralityof through holes 11H are provided on a vicinity of a center of the upperdie clamp 11 in the vertical direction, a mounting bolt 41 pierces thethrough holes 11H and is screwed up and fixed to a left side of theupper die supporting section 9 horizontally in FIG. 5, and a coil spring43, which biases the upper die clamp 11 to a direction where the upperdie clamp 11 is always pressed, is set resiliently so that the upper dieclamp 11 is held on a head portion of the mounting bolt 41. As a result,the upper die clamp 11 is supported in the rocking manner.

Further, a mounting nut 45 which pierces the through holes 11 on theupper die clamp 11 on a right side in FIG. 5 is screwed up and fixed toa screw portion of the mounting bolt 41 which projects horizontally tothe right side of the upper die supporting section 9 in FIG. 5, and thecoil spring 43, which biases the upper die clamp 11 to a direction wherethe upper die clamp 11 is always pressed, is set resiliently so that theupper die clamp 11 is held on the head portion of the mounting nut 45.As a result, the upper die clamp 11 is supported in the rocking manner.

Here, touching portions between the head portions of the mounting bolt41 and the mounting nut 45 and the through holes 11H are formed into aspherical contact surface so that the upper die clamps 11 rockssmoothly.

With reference also to FIG. 8, a locking projection 11P, which freelylocks into a drop-proof groove 5G in the horizontal direction formed onthe upper portion of the upper die 5, is formed on a lower end of theupper die clamp 11 so as to project towards the upper die supportingsection 9. A pressing member 47, which touches an inclined plane 5S ofthe upper section 5U of the upper die 5 so as to press the upper die 5against the upper die supporting section 9, is provided to a slightlyupper portion of the locking projection 11P.

The pressing member 47 has a form obtained by working a part of aperipheral surface of a circular cylinder into a plane, and the pressingmember 47 is mounted to the lower portion of the upper die clamp 11 viaa plurality of screws 49 in a slightly rotatable manner.

Further, a wedge piece 51 (locking member) which is freely engaged withthe drop-proof groove 5G of the upper die 5 is provided on an upperportion of the locking projection 11P and between the pressing member 47and the locking projection 11P so as to freely advance and retreat. Thewedge piece 51 is always biased so as to be engaged with the drop-proofgroove 5G by a function of a resilient member 53 such as a coil springresiliently set between the wedge piece 51 and the upper die clamp 11.

Movement of the wedge piece 51 by means of the biasing force isrestrained in such a manner that a part of the wedge piece 51 touches apart of the pressing member 47, and an inclined plane 51S is formed onan upper surface of an edge of the wedge piece 51 so that the wedgepiece 51 is easily engaged with and disengaged from the drop-proofgroove 5G.

With reference also to FIG. 3, the clamping force applying means 13,which applies the clamping force for pressing and fixing the upper die 5to the upper die supporting section 9 using the pressing member 47provided on the lower portion of the upper die clamp 11 to the upper dieclamp 11, is included in a cylinder 55 in the front-rear directionprovided on the block section 7B of the holder body 7.

More specifically, the clamping force applying means 13 is constitutedso that both sides in the front-rear side of the cylinder 55 are blockedby cover sections 55C, respectively, and two pistons 57 are providedslidably to the front-rear direction in the cylinder 55. A pin-shapedpusher section 57P is projected to the outside of the cylinder 55 fromthe pistons 57, and the pusher sections 57P project outward from thethrough holes 55H provided on the cover sections 55C. Tips of the pushersections 57P can touch and separate from a pressing screw 59 as apressure receiving member provided on the upper portion of the upper dieclamp 11.

Further, a resilient member 61 such as a coil spring as a membercomposing a part of the clamp switching means 15 for biasing the piston57 to a direction where it is always pressed inward is wound around thepusher sections 57 of the pistons 57. Moreover, an oil passage 63 whichcommunicatively connects with the inside of the cylinder 55 between thetwo pistons 57 is formed on the block section 7B of the holder body 7,and the oil passage 63 is communicatively connected with a pressure oilsupply port 65 provided on a sidewall surface of the block section 7B.The pressure oil supply port 65 is communicatively connected with apressure oil supply source (not shown) via a hydraulic hose 67.

In a releasing state holding means 19 which freely holds the upper dieclamp 11 in a state that the clamp of the upper die 5 is released, asshown in a cross section on the left side of FIG. 5, a spring support69, which is engaged with a locking hole section 11G formed on the upperportion of the upper die clamp 11 via a resilient member 11S such as aspring, is fixed to the holder body 7, and the upper portion of theupper die clamp 11 is biased to a direction where it is always pressedto the holder body 7 by the resilient member 11S.

The pressure receiving member which constitutes a main section of themode of the present invention is detailed below.

With reference to FIG. 3, an elliptical notched portion 11C which islong in the vertical direction (see FIGS. 6 and 7) is provided on a leftsurface in FIG. 3 on the upper portion of the upper die clamp 11, forexample, and a tapped hole 11N which pierces the notched portion 11C isprovided. The pressing screw 59 as the pressure receiving member isscrewed into the tapped hole 11N so as to freely advance and retreat,and a tip on the left side in FIG. 3 of the pressing screw 59 has apressure sensing surface 59P which is pressed by the pusher section 57Lof the piston 57.

A position lever shaft section 71 is screwed up to an end surface on theleft side in FIG. 3 of the pressing screw 59 by a mounting bolt 71B, andthe position lever shaft section 71 can be rotated in the notchedportion 11C in a state that its outer peripheral surface isapproximately screwed into an upper semicircular side wall surface ofthe notched portion 11C. Moreover, a groove section 71G for a ring isprovided along the outer peripheral surface of the position lever shaftsection 71, and a stopper ring 73 for restraining rotation of theposition lever shaft section 71 to 180° is fitted into the groovesection 71G for ring. The stopper ring 73 has a shape such that itslower side in FIG. 7 expands outward from the groove section 71G forring. When the position lever shaft section 71 rotates by 180°, theexpanded portion of the stopper ring 73 touches the upper side wallsurface of the notched portion 11C so that the rotation is restrained.

A notched portion 71C for mounting a lever is provided on the lower sidein FIGS. 3 and 6 of the position lever shaft section 71, and a positionlever 75 which has a shape fitted into the notched portion 71C isscrewed up to the position lever shaft section 71. Moreover, a magnet75M is buried in a right surface in FIG. 3 of the position lever 75, anda spring pin 71P made of iron, for example, as a magnetic material whichis attracted to the magnet 75M is buried in an area from the positionlever shaft section 71 to the pressing screw 59.

With the above constitution, in the state of FIG. 3, when the magnet 75Mis separated from the spring pin 71P and the position lever 75 is liftedup so as to be rotated by 180°, also the position lever shaft section 71is rotated by 180°, thereby rotating also the pressing screw 59. As aresult, as shown in FIG. 4, the pressure sensing surface 59P of thepressing screw 59 moves from a position represented by an alternate longand short dash line to a position represented by a solid line. Accordingto the rotation of the position lever shaft section 71, the expandedportion of the stopper ring 73 touches the upper sidewall surface of thenotched portion 11C so that the rotation by 180° is restrained. When theposition lever 75 is returned to its original position, the positionlever 75 is attracted to the spring pin 71P via the magnet 75M so as tobe fixed to the position lever shaft section 71.

As mentioned above, selection is freely made from a first stage wherethe pressure sensing surface 59P of the pressing screw 59 is advancedtowards the pusher section 57P as shown in FIG. 3 and a second statewhere the pressure sensing surface 59P is retreated from the side of thepusher section 57 as shown in FIG. 4 by rotating the position lever 75by 180°. That is to say, an opening quantity of the upper die clamp 11at the time of unclamping can be freely selected from the two stages.

In the above constitution, as the upper die 5 is shown by an imaginaryline in FIG. 5, when pressure oil is supplied into the cylinder 55 inthe clamping force applying means 13 in a state that the upper die 5 isclamped between the upper die supporting section 9 of the holder body 7and the upper die clamp 11, the pistons 57 advance outward against thebiasing force of the resilient member 61 and the tips of the pushersections 57P touch the pressing screw 59 of the upper die clamp 11, sothat a pressing force (clamping force) of the cylinder 55 is transmittedthereto.

The upper die clamp 11 on the left side in FIG. 5 is moved rotationallyto a counterclockwise direction and the upper die clamp 11 on the rightside in FIG. 5 is moved rotationally to a clockwise direction by thepressing force (clamping force) of the cylinder 55, and the upper dieclamp 11 presses and fixes the upper die 5 more strongly.

On the contrary, when the pressure oil in the cylinder 55 is discharged,the pistons 57 retreat inward due to the biasing force of the resilientmember 61, and the tips of the pusher sections 57P move so as toseparate from the pressing screw 59 of the upper die clamp 11 so thatpressing force (clamping force) of the cylinder 55 is released.

As shown in the cross section on the left side in FIG. 5, therefore, theupper portion of the upper die clamp 11 is moved to the holder body 7 bythe resilient member 11S of the spring support 69, so that the pressingscrew 59 on the upper portion of the upper die clamp 11 lightly touchesthe pusher sections 57P of the clamping force applying means 13, so thatthe pressing and fixing of the upper die 5 by the upper die clamp 11 arereleased. The upper die 5 is supported so as to be movable to alongitudinal direction (horizontal direction) in a state that thelocking projection 11P of the upper die clamp 11 is engaged with thedrop-proof groove 5G.

In such a manner, since the upper die clamp 11 is easily operated by thecylinder 55 (liquid pressure device), the upper die 5 is attached to anddetached from the holder body 7 efficiently.

That is to say, the lower portion of the upper die clamp 11 is opened soas to separate from the upper die supporting section 9, so that theupper die 5 can be detached from the upper die clamp 11 so as to bereplaced.

More specifically, at the first stage in FIG. 3, the opening quantity ofthe upper die clamp 11 at the time of unclamping becomes smaller thanthat at the second stage in FIG. 4 because the position of the pressuresensing surface 59P of the pressing screw 59 advances. The engaged statebetween the wedge piece 51 and the drop-proof groove 5G of the upper die5 at this time is such that even if the upper die 5 is tried to be drawndownward against the biasing force of the resilient member 53 to thedirection of the upper die supporting section 9 of the wedge piece 51,the tip of the wedge piece 51 projects further than the engagingprojection 112 at the lower end of the upper die clamp 11, therebypreventing the upper die 5 from being drawn. So to speak, the upper die5 cannot be front-fed and front-removed. The upper die 5 can be,however, drawn to the lateral direction.

Further, when the position lever 75 is rotated by 180° so as to be atthe second state in FIG. 4, the position of the pressure sensing surface59P of the pressing screw 59 retreats, so that the opening quantity ofthe upper die clamp 11 at the time of unclamping is larger than that atthe first stage in FIG. 3. The engaged state of the wedge piece 51 withthe drop-proof groove 5G at this time is such that the upper die 5 canbe drawn downward against the biasing force of the resilient member 53towards the upper die supporting section 9 of the wedge piece 51. Thatis to say, the tip of the wedge piece 51 retreats further than thelocking projection 11P at the lower end of the upper die clamp 11, sothat the upper die 5 can be drawn downward. Moreover, on the contrary,the upper section 5U of the upper die 5 can be inserted between theupper die supporting section 9 of the holder body 7 and the upper dieclamp 11 from a lower direction. So to speak, the upper die 5 can befront-fed and front-removed.

According to the above constitution, even if the upper die 5 is slidmightily and thus a stronger force than the biasing force of theresilient member 53 of the wedge piece 51 is applied to the upper die 5at the time of replacing, the position levers 75 can be switched intothe first stage, so that a danger such that the upper die 5 drops evennot at the time of first-feeding and first-removal is eliminatedcompletely. Moreover, the position lever 75 is switched into the secondstage, so that the upper die 5 can be easily front-fed andfront-removed.

By the way, in this mode, since a stroke of the cylinder 55 is about 3mm, a mechanism having two-stage stroke can not be incorporated into thecylinder 55, and there is generally a limit in incorporating of thecylinder 55 with large stroke due to a thickness of the holder body 7.Moreover, since the 6 to 30 upper die holder apparatuses 1 are attachedto the press brake, the clamping force of the cylinder 55 differsaccording to individual difference between the upper die holderapparatuses 1, and thus an accurate operation cannot desired.

In this mode, however, the two-stage unclamping operation can beperformed securely only by a simple operation for rotating the positionlever 75 by 180°. Since the press brake has a plurality of the upper dieholder apparatuses 1, the simplicity of the switching operation isgreatly effective from a viewpoint of operability.

The present invention is not limited to the examples of the mode, andanother modes can be carried out by making suitable modifications.

1. An upper die holder apparatus, comprising: a holder body; an upperdie clamp supported to the holder body with a supporting pointsupporting said upper die clamp in a vicinity of a center in a verticaldirection of the holder body; a clamping force applier provided to theholder body and pressing an upper portion of the upper die clamp so thatthe upper die clamp clamps the upper die; and a pressure receiverprovided to an upper portion of the upper die clamp and having apressure sensing surface to be pressed by the clamping force applier,wherein the pressure receiver is provided so that its advancing andretreating are adjusted to a pressing direction by the clamping forceapplier; and wherein the pressure receiver is provided so that anopening amount of the upper die clamp at the time of unclamping isfreely selected between a plurality of stages.
 2. The upper die holderapparatus according to claim 1, further comprising: an upper die supportprovided to a lower portion of the holder body and supporting an upperdie; a presser provided to a lower portion of the upper die clamp andpressing the upper die against the upper die support; and a lock memberprovided to a lower portion of the upper die clamp and being biasedtowards the upper die support so as to freely lock into a drop-proofgroove provided to the upper die.
 3. The upper die holder apparatusaccording to claim 2, wherein the opening amount of the upper die clampat a time of unclamping is adjustable so that a locked state between thelocking member and the drop-proof groove of the upper die is freelyselected from a first stage where the upper die cannot be drawn downwardand a second stage where the upper die can be drawn downward.
 4. Theupper die holder apparatus according to claim 3, wherein the pressurereceiver is screwed into the upper portion of the upper die clamp; andwherein a position lever which is rotated so as to advance and retreatthe pressure receiver is provided gradationally to the pressurereceiver.